The proposed research consists of a seris of neuroanatomical experiments on cortical-subcortical interconnections of the rabbit visual system. Two neuroanatomical techniques will be used to trace these pathways: the autoradiographic procedure utilizes the anterograde axonal transport of tritiated amino acid to define efferents of a @articular area; and retrograde axonal transport of horseradish peroxidase (HRP) is used to identify afferents to an area. Corticofugal pathways will be studied by injecting HRP bilaterally into either the lateral geniculate nucleus, the pulvinar, the pretectum or the superior colliculus and the retrogradely labeled visual cortical cells will be identified. This data will indicate: a) the cortical cells which project to each of the subcortical nuclei, b) the laminar distribution of these cells, c) the area distribution of corticofugal cells, and d) the differential distribution of visual cortical cells which project on the nuclei so injected. The rabbit techtothalamic projections will be investigated by injections of tritiated amino acid into the superior colliculus as well as by thalamic injections of HRP. The specific goals of this series are: a) to describe the location of the cells of the superior colliculus which project upon the pulvinar and upon the lateral geniculate nucleus, and b) to delimit precisely the projections of the superior colliculus on the dorsal thalamus. The thalamocortical portion of the visual system of the rabbit will be studied by injections of tritiated amino acid into the lateral geniculate nucleus and pulvinar. The objective of this experimental series is: a) to directly demonstrate the projection of the dorsal lateral geniculate nucleus to the cortex, b) to study the projection of the pulvinar upon the cortex, and c) to study the overlap or lack of overlap of these two projections. The results of these experiments will contribute to the accumulating evidence on the rabbit visual system and, thereby, will add to findings in other animals on the comparative morphology of the visual system.